K64F/Kinetis: extract_dts_includes.py warnings when building sample

[mike-scott]

Example warnings when building LwM2M client for K64F:

-- Generating zephyr/include/generated/generated_dts_board.h
extract_dts_includes.py: 'id' property missing in 'Kinetis Pinmux' binding. Using '<unknown id>'.
extract_dts_includes.py: Merge of 'description': 'Clock gate control information'  overwrites 'Clock gate information'.
extract_dts_includes.py: Merge of 'generation': 'structures'  overwrites 'define'.
extract_dts_includes.py: 'id' property missing in 'Kinetis GPIO' binding. Using '<unknown id>'.
extract_dts_includes.py: 'id' property missing in 'Kinetis I2C Controller' binding. Using '<unknown id>'.
extract_dts_includes.py: Merge of 'description': 'Clock gate control information'  overwrites 'Clock gate information'.
extract_dts_includes.py: Merge of 'generation': 'structures'  overwrites 'define'.

[mike-scott]

@MaureenHelm thanks!